Stabilized powdered formaldehyde

ABSTRACT

According to an aspect of the invention, a polymerized form of formaldehyde is available in granular form containing a polymerized form of formaldehyde, such as paraformaldehyde, a buffer, such as sodium phosphate dibasic anhydrous, and a stabilizer, such as hydroxymethyl cellulose, or hydroxypropyl methyl cellulose. When added to an aqueous solvent, the paraformaldehyde can dissolve in alkaline solution, and depolymerizes into a formaldehyde solution containing a stabilizer. Optionally a second member of the buffer pair or another buffer or pH adjuster can be used The stabilized depolymerized formaldehyde solution is then ready for use, or can be modified by addition of other substances, such as sodium phosphate monobasic monohydrate. Additionally, an additional buffer may be included in the granular mixture to increase the rate at which the solid dissolves and depolymerizes.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/357,596, filed Feb. 4, 2003, which claims the benefit of U.S.Provisional Patent Application No. 60/355,730, filed Feb. 5, 2002, bothof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is related to powdered formalin for uses in thefields of histology, particularly fixatives used in clinical andhistology laboratories, and of chemistry, including the production ofplastics and polymerized forms of aldehydes, and more particularly topowdered forms, and to methods for their manufacture and use.

BACKGROUND

Aldehyde solutions are produced and used for a wide variety of purposes.For example, formaldehyde (CH₂O) is a widely manufactured andtransported chemical for use as a fixative in clinical and histologylaboratories. Formaldehyde may be purchased and delivered as a 37%liquid solution with approximately 12% to approximately 15% methanoladded. This product may then be diluted, often in water, to anapproximately 3.7% solution for fixation purposes, such as fixation oftissue. Typically, a fixative is used to preserve biological specimenssuch as biopsy or tissue specimens, for medical diagnosis.

Additionally, formaldehyde may be produced in a concentrated liquid formfor producing a variety of polymers and resins. These polymers andresins may include linear polymers, lower polyoxymethylene glycols,paraformaldehyde, alpha-polyoxymethylene, beta-polyoxymethylene,polyoxymethylene glycol derivatives, polyoxymethylene diacetates,polyoxymethylene dimethyl ethers, gamma-polyoxymethylene,delta-polyoxymethylene, epsilon-polyoxymethylene, high molecular weightpolyoxymethylenes, aceteal resins, cyclic polymers, and tetraoxane.

Formaldehyde solutions may be produced by heating solid formaldehydepolymers with water. Using a heating technique, formaldehyde solutionsabove 50% by weight of formaldehyde can be obtained from solidformaldehyde polymers. Concentrations of liquid formaldehyde above about50% precipitate at about “room temperature” (approximately 25° Celsius)as polymers of formaldehyde. The temperature necessary to maintain aclear solution and prevent separation of solid polymer increases fromroom temperature to about 100° Fahrenheit as the solution concentrationis increased to about 37%.

Additionally, there are several other disadvantages to the process ofdiluting and storing formaldehyde in liquid form.

Processes for making formaldehyde solutions are hazardous and difficultto perform.

Processes for making formaldehyde solutions often require specializedequipment which is often not available to clinical or histologylaboratories. For example, in liquid form there has to be adequateventilation with protective mechanisms to prevent inhalation of vapors.

Additionally, 37% formaldehyde solutions must be stored at no lower thanroom temperature conditions, otherwise the solutions can loseeffectiveness and become unstable if stored for an extended period oftime.

Processes of producing and storing other aldehyde solutions oftenexhibit similar difficulties and disadvantages.

There are also several other disadvantages to the process of heatingformaldehyde polymers to generate formaldehyde solutions.

Processes for producing and storing aldehyde solutions are hazardous anddifficult to perform.

Processes for producing and storing aldehyde solutions often requirespecialized equipment which is often not readily available. For example,in liquid form there has to be adequate ventilation with protectivemechanisms to prevent inhalation of vapors.

As a result of the above disadvantages, currently liquid aldehydesolutions are frequently produced at a manufacturing facility and thentransported to an end user. However, transporting liquid aldehydesolutions is expensive and dangerous. Containers are large, heavy andmay rupture during transport thereby exposing other individuals to thedangerous solution.

Accordingly, an easier, safer technique for producing, storing andtransporting aldehydes, such as formaldehyde, for a variety of purposesis desirable.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

According to an aspect of the invention, a polymerized form of aldehydeor other fixative is available in granular form containing a polymerizedform of the fixative and at least one buffer, such as a basic componentof a buffer pair. When added to an aqueous solvent, the polymerizedfixative dissolves thereby forming a solution of the fixative. Thesolution is then ready for use, or can be modified by addition of othersubstances. For example, a stabilizer may be added.

According to another aspect of the invention, a composition contains agranular form of formaldehyde, such as paraformaldehyde, a buffer, suchas sodium phosphate dibasic anhydrous, and a stabilizer, such ashydroxymethyl cellulose, or hydroxypropyl methyl cellulose. When addedto an aqueous solvent, the paraformaldehyde dissolves, and depolymerizesinto a formaldehyde solution containing a stabilizer. The stabilizeddepolymerized formaldehyde solution is then ready for use, or can bemodified by addition of other substances, such as sodium phosphatemonobasic monohydrate.

According to still another aspect of the invention, a polymerized formof formaldehyde is available in granular form containing a polymerizedform of formaldehyde, such as paraformaldehyde, a combination ofbuffers, such as sodium phosphate dibasic anhydrous and sodiumhydroxide, and a stabilizer, such as hydroxymethyl cellulose, orhydroxypropyl methyl cellulose. When added to an aqueous solvent, theparaformaldehyde dissolves, and depolymerizes into a formaldehydesolution containing a stabilizer. The stabilized depolymerizedformaldehyde solution is then ready for use, or can be modified byaddition of other substances, such as sodium phosphate monobasicmonohydrate.

In still other aspects, other fixatives, such as acetaldehyde,propionaldehyde, and other aldehydes can be prepared according to thisinvention. In general, any fixative that can be in a solid form underconditions of storage and use can be prepared using the methods of thisinvention.

DESCRIPTION OF THE DRAWINGS

The invention will be described with respect to the particularembodiments thereof. Other objects, features, and advantages of theinvention will become apparent with reference to the specification anddrawings in which:

FIG. 1 is a table of some formaldehyde polymers;

FIG. 2 is a graph which illustrates the effect of pH on aqueoussolubility of paraformaldehyde;

FIG. 3 is a graph which illustrates the effect of pH on paraformaldehydeaqueous solubility constant; and,

FIG. 4 illustrates a commercial embodiment of the present invention.

DETAILED DESCRIPTION

For explanation purposes, embodiments of the present invention will bedescribed with respect to the aldehyde, formaldehyde, but it will beunderstood that other embodiments of the present invention may includeother solid forms of polymerized aldehydes, other types of histologicalfixatives, and other reactive compounds. In general, embodiments of thisinvention include a dry preparation of an aldehyde or other reactiveagent and a stabilizer.

Paraformaldehyde is a polymer that, upon de-polymerization can formformaldehyde. Polymer formation is one of the characteristic propertiesof the formaldehyde molecule. As indicated by the structures shownbelow, two fundamentally different polymer types for formaldehyde arepossible..CH₂.O.CH₂.O.CH₂.O.CH₂.O.CH₂.O....   (1)

Linear formaldehyde polymers, as illustrated by structure (1) arereversible polymers (i.e., may be polymerized and de-polymerized) andreact chemically as solid forms of formaldehyde. Representatives ofstructure (2) are encountered in polyhydroxyaldehydes.

Linear polymers range from the low molecular weight water-solubleoligo-oxymethylenes (“OOM”) to the high molecular weightpolyoxymethylenes (“POM”). Low molecular weight polymers, or OOMs, aretypically obtained from an aqueous formaldehyde solution by a series ofcondensation or additive reactions involving methylene glycol. Lowmolecular weight polymers are brittle solids that depolymerize toproduce formaldehyde in a form that is substantially free of water. Highmolecular weight polymers, or POMs, are generally produced by thepolymerization of the anhydrous monomer or the cyclic trimer trioxane.

Commercial formaldehyde polymers typically include a mixture of linearpolymers, such as HO(CH₂O)_(n.H), the cyclic trimer (CH₂)O)₃, trioxaneand the POM or polyformaldehyde plastics also known as acetal resins offormaldehyde.

High molecular weight linear formaldehyde polymers generally includepolyoxymethylene glycols (“POMG”) and their derivatives.Polyoxymethylene glycols are hydrated polymers chemically andstructurally related to methylene glycol. Although some of the POMGs maybe isolated in comparatively pure state, POMGs are usually encounteredas molecular weight mixtures, the formaldehyde content of which is ameasure of the average degree of polymerization. On the basis ofmolecular weight, physical properties, and methods of preparation, POMGsmay be classified into three groups: 1) the lower POMGs oroligo-oxymethylene glycols (“OOMG”), 2) paraformaldehyde and 3)alpha-polyoxymethylene. It is to be noted however that thisclassification is more or less arbitrary and is only made for purposesof convenience. The three groups merge into one another on the basis ofdegree of polymerization and absolute dividing lines cannot be drawnbetween them.

In general, POMGs have the appearance of colorless powders possessing acharacteristic odor of formaldehyde. POMGs properties such as meltingpoint, solubility, chemical reactivity, etc., vary with molecularweight. As the degree of polymerization, indicated by n in the formula,HO(CH₂O)_(n.H) increases, the formaldehyde content approaches 100% andthe physical and chemical properties approach those of thepolyoxymethylenes. FIG. 1 illustrates a table of some of the linearformaldehyde polymers.

When aqueous formaldehyde solutions containing from approximately 30% toapproximately 80% formaldehyde are brought to room temperature or below,a precipitate consisting principally of the lower molecular weight POMGcan be obtained. The point at which precipitation takes place can dependon the concentration of the formaldehyde solution, the temperature, thesolvent, and/or the rate of cooling, among others.

The lower molecular weight POMGs, or OOMGs, are colorless solids meltingin the range from about 80° C. to about 120° C. Polyoxymethylene glycolsand OOMGs differ from paraformaldehyde and other higher homologs inbeing soluble in acetone and ether, and by dissolving with little or nodecomposition. Polyoxymethylene glycols and OOMGs dissolve slowly inwarm water with hydrolysis and/or other depolymerization reactions toform formaldehyde solutions. Polyoxymethylene glycols and OOMGs areinsoluble in petroleum ether or other non-polar solvents.

Paraformaldehyde, as described herein, is a mixture of POMGs containingfrom about 90% to about 99% formaldehyde and a balance consistingprincipally of free and combined water. Polyoxymethylene glycols cancontain from about 6 to about 100 formaldehyde units per molecule. Themajority of the polyoxymethylene glycols in paraformaldehyde containover 12 formaldehyde units per molecule. The chemical composition ofparaformaldehyde can be expressed by the formula HO(CH₂O)_(n.H). Commongrades of paraformaldehyde include flaked and powdered materials havinga minimum formaldehyde content of about 91% and powdered as well asgranular grades having about a 95% minimum. Special grades of relativelyhigh molecular weight paraformaldehyde may have a formaldehyde contentof over 98%.

At ordinary temperatures, paraformaldehyde can gradually vaporize, andon long exposure to the atmosphere complete volatilization caneventually take place. Ultrasonic waves can also partially depolymerizeparaformaldehyde. Sequential depolymerization can take place from thehydroxyl end of the molecule of paraformaldehyde as illustrated anddescribed below.—CH₂—O—CH₂—O—CH₂OH→—CH₂—O—CH₂—OH+CH₂O

The rate of depolymerization can depend on the number and availabilityof end groups. Thus, a high molecular weight polymer depolymerizes toformaldehyde more slowly than one of low molecular weight although therate of the depolymerization can be the same for each. At the same time,the rate of depolymerization of a high molecular weight polymer, the endgroups of which are at the outside of the polymer bundles, will differfrom the rate of depolymerization of a high molecular weight polymer,the end groups of which are buried within a tangled mass of polymerchains.

As a result of such depolymerization mechanisms, liberation of watervapor from the polymer is a result of the chain degradation in whichPOMG breaks down to water and formaldehyde.

Paraformaldehyde dissolves in water, hydrolyzing and depolymerizing asit dissolves. The rate of depolymerization depends upon the temperatureof the water. In general, at room temperature, it takes weeks at roomtemperature to depolymerize paraformaldehyde into formaldehyde withinwater. It takes even longer to depolymerize paraformaldehyde intoformaldehyde in colder water. For example, a 28% formaldehyde solutionmay be obtained by agitating paraformaldehyde in water at about 18° C.for five weeks. Formaldehyde solutions obtained in this way areidentical with those obtained by dissolving gaseous formaldehyde inwater. It can be appreciated that the rate of depolymerization canincrease in solutions at higher temperature. Any temperature can beused, but conveniently, temperatures below boiling are convenient. Suchtemperatures can be from room temperature to about 100° C. Hot waterbaths or double-boilers can be used in many settings, includinglaboratory or hospital settings.

It can be appreciated that under reflux conditions at elevatedtemperatures almost any desired concentration of formaldehyde can beobtained within a few hours. However, solutions obtained in this way areoften cloudy due to incomplete depolymerization.

Depolymerization of polymeric formaldehyde can be influenced by pH. Thehydrogen and hydroxide ion concentrations of the solution have aconsiderable influence on the rate of depolymerization. Depolymerizationis at a minimum in the pH range of about 2.6 to about 4.3, and increasesrapidly with higher or lower pH values as is illustrated in FIGS. 2 and3. The rate of depolymerization can be increased more under alkalineconditions than acidic conditions, as hydroxyl ions can exert 10⁷ timesstronger effects on depolymerization than hydrogen ions. At lowtemperatures, (e.g., about 25° C. and below) depolymerization offormaldehyde polymers is a slow reaction. Solutions in the pH rangeabout 2.6 to about 4.3 require more than 50 hours to attain equilibriumafter reduction of formaldehyde polymers from about 36.5% to about 3% atabout 0° C. Methanol and similar substances that lower the ion productof water also lower the rate of depolymerization of polymericformaldehyde.

In contrast to the relatively slow depolymerization in near-neutralconditions, dilute alkali and acids accelerate the rate ofdepolymerization of paraformaldehyde.

Measurements of the rate of depolymerization of paraformaldehyde inwater show that at low concentrations of formaldehyde the reaction ofdepolymerization of paraformaldehyde is kinetically a monomolecularreaction. However, as the formaldehyde concentration increases, reversereactions of a higher order occur, for example dissolved formaldehydecondenses and forms higher molecular weight homologs of polyoxymethyleneglycols.

Mechanism of the hydrolytic depolymerization reactions of formaldehydepolymers differ under alkaline and acidic conditions. Under alkalineconditions, degradation proceeds in a stepwise fashion: formaldehydeunits successively split from the ends of the linear POM molecule. Underacidic conditions, oxygen linkages within the molecular chain can beattacked by hydrogen ions, and large molecules can be split into smallerfragments.

The rate at which paraformaldehyde and other POMGs dissolve in water canreflect the degree of polymerization. Rate measurements ofdepolymerization of POMGs in water accordingly provide a useful methodto compare the degree of polymerization of paraformaldehyde, alphapolyoxymethylene, and other polymers of this type.

An embodiment of the present invention provides a method for producing asolid mixture including a polymerized aldehyde, and at least one basicbuffer which may be combined with an aqueous solution to form a solutioncontaining a desirable concentration of the depolymerized aldehyde at analkaline pH. A stabilizer may also be included in the original solidmixture or added to the solution to prevent the depolymerized aldehydefrom repolymerizing.

Paraformaldehyde can be used to make compositions of this inventioneither “as is” from the manufacturer, or if desired, the material can befurther pulverized to increase the surface area:volume ratio. Increasingthe surface area:volume ratio can increase the speed with whichpolymerized paraformaldehyde depolymerizes. Furthermore, in dry-mixingprocesses, a pulverizer may be employed to decrease the size ofparticles of paraformaldehyde and/or buffer and/or stabilizer. Suchpulverizers and methods for using them are known in the art and need notbe described herein further.

The use of a first, basic member of a buffer pair (e.g., PO₄.⁻², or CO₃⁻²) can be especially useful because with such a member of a bufferpair, alkaline hydrolysis can be promoted, and then subsequently, whenthe desired degree of depolymerization is obtained, the second member ofthe buffer pair (e.g., H P₄— and H CO₃—, respectively) can be added toadjust the pH and the buffering capacity to within a desired workingrange.

Although buffers can be used that have any degree of hydration (e.g.,coordinated with a certain number of moles of water per mole of buffercomponent), in some cases it can be desirable to use anhydrous buffers(e.g., those that contain no coordinated water molecules). Hydratedsubstances can liberate water to other components of the system, and thepresence of water can result in partial depolymerization ofparaformaldehyde, and therefore may liberate formaldehyde gas, which canbe toxic.

Once the solution is formed, in an embodiment, a second solid buffer maybe added to the solution to control the pH, osmolality, osmolarity,isotonic pressure of the solution, etc.

For example, one of the POM's, such as paraformaldehyde, may be combinedwith a solid alkaline buffer, such as sodium phosphate dibasicanhydrous. It can be desirable for the buffer material to have arelatively large surface area:volume ratio, to promote more rapidsolubilization in aqueous media. When mixed with water at roomtemperature, the buffer produces a solution having a basic (alkaline) pHand the paraformaldehyde rapidly depolymerizes to a formaldehydemonomer. A stabilizer, such as hydroxypropyl methyl cellulose may alsobe included in the solid mixture or added after the solid mixture hasbeen combined with water. The stabilizer will keep the formaldehyde fromreversing back to paraformaldehyde.

In an alternative embodiment, more than one basic material may beincluded in the solid mixture. For example, in addition to the basicbuffer sodium phosphate dibasic anhydrous, a second basic buffer, suchas carbonate or a base such as sodium hydroxide may also be included.The inclusion of a second basic material, can further increase the rateof depolymerization of the aldehyde when combined with water. Theaddition of additional buffers also affects the pH value of thesolution. Thus, to increase the pH of the solution, one can use a base,such as hydroxide ion, instead of using another member of a buffer pair(e.g., carbonate).

Other examples of materials which may be used individually or incombination include, but are not limited to, ammonium hydroxide,ammonium acetate, sodium acetate, lithium carbonate, lithium hydroxide,sodium bicarbonate, sodium carbonate, sodium citrate, and Tris(hydroxymethyl aminomethane) free base.

Stabilizers may be used to inhibit depolymerized aldehyde fromrepolymerizing. Stabilizers include, but are not limited to,hydroxymethyl cellulose, gelatin, pectin, carrageenan, polyoxymethyleneethers of higher fatty acids, hydrazine hydrate, hydroxylaminehydrochloride, and acidic nitrogen compounds (e.g., urea, melamine), andhydrogen sulfide.

If controlling the pH, osmolality, osmolarity, and isotonic pressure ofthe solution is desirable, a second member of the buffer pair, such assodium phosphate monobasic monohydrate (for use with dibasic phosphateions) may be added to the resultant solution. Alternatively, otherbuffers such as potassium phosphate monobasic (KH₂PO₄), sodium phosphatemonobasic (NaH₂PO₄), and Tris (hydroxymethyl aminomethane) free base(HCl), or bicarbonate (HCO₃—; used with carbonate ions CO₃ ⁻²) may alsobe used to control pH, osmolality, osmolarity, and isotonic pressure.

The selection of a buffer for physiological or histological purposes candepend upon the pH to be desired of the final solution. Thus, bufferpairs can be selected that have a pK near the working pH. The p of abuffer is the pH at which the concentrations of the buffer “base” (e.g.,PO₄ ⁻²) is equal to the buffer “acid” (e.g., PO₄—). Buffering capacity(e.g., the ability to maintain pH in the face of increased acid oralkaline load) of a buffer solution is maximized when the concentrationsof the buffer pairs are equal. Thus, in situations in which neutralsolutions are desired (e.g., histological purposes), phosphate bufferscan be desirable because the pK of a phosphate buffer system is about6.8. However, one can use a buffer pair in a pH range within about 2 pHunits so long as the concentration of the relevant acceptor of the pairis in sufficiently high free concentration to react with the acid oralkaline load. Numerous buffer pairs are known in the art and need notbe described herein in detail.

In addition to using buffers, other materials may be included to adjustosmotic concentration of an aldehyde solution. For example, glucose,sucrose, mannitol, or salts (e.g., NaCl, KCl, etc) can be added. Forfixation of biological samples, it can be desirable to use an isoosmolarsolution (e.g., about 300 mOsm/L) or a slightly hyperosmolar solutions(e.g., slightly above about 300 mOsm/L). However, for fixation of othertissues, a more hyperosmolar solution can be used so long as therelationships between cells and tissues is not disrupted. For industrialuses, such as manufacture of plastics, concretes etc. the osmolarity ofthe solution can be selected as desired.

FIG. 4 illustrates an embodiment of the present invention which may becommercially distributed for producing a stabilized solution offormaldehyde. The embodiment described with respect to FIG. 4 may beused to easily produce one liter of a stabilized solution having aconcentration of about 3.7% formaldehyde with a pH of about 6.85.

A kit 400 includes a first packet 401 containing a powdered mixturewhich includes approximately thirty-seven (37) grams of paraformaldehydeand approximately six and one half (6.5) grams of sodium phosphatedibasic anhydrous. A second packet 402 contains approximately four (4)grams of sodium phosphate monobasic monohydrate. Approximately 0.01grams of hydroxypropyl methyl cellulose may be included in either packetas a stabilizer.

In producing a formaldehyde solution, the contents of the first packet401 are mixed with one (1) liter of water, preferably at roomtemperature, and stirred until the powdered solution is dissolved. Aftermixing, a solution having a concentration of about 3.7% formaldehydewith a pH of about 10.5 is produced.

The contents of the second packet 402 may then be added and mixed untildissolved. The resulting solution has a concentration of about 3.7%formaldehyde and a pH of about 6.85. For histology purposes, thesolution also has desirable osmolality, osmolarity, and isotonicpressure which protects tissue to be fixed with the solution.

In an alternative embodiment, the kit 400 may include more than onebuffer in the first packet 401 thereby further effecting the rate ofdepolymerization and pH when combined with water. For example, and againdescribing the kit 400 for use in producing one (1.0) liter ofstabilized solution, the powdered mixture of the first packet 401includes approximately thirty-seven (37) grams of paraformaldehyde,approximately four (4.0) grams of sodium phosphate dibasic anhydrous,and approximately one (1.0) gram of sodium hydroxide. A second packet402 contains approximately six and one half (6.5) grams of sodiumphosphate monobasic monohydrate. Approximately 0.01 grams ofhydroxypropyl methyl cellulose may be included in either packet as astabilizer.

As described above, in producing a formaldehyde solution, the contentsof the first packet 401 are mixed with one (1) liter of water,preferably at room temperature, and stirred until the powdered solutionis dissolved. The addition of sodium hydroxide in the first packet 401increases the rate at which the powdered solution is dissolved andincreases the pH of the resulting solution. After mixing, a solutionhaving a concentration of about 3.7% formaldehyde with a pH of about11.2 is produced.

The contents of the second packet 402 may then be added and mixed untildissolved. The resulting solution has a concentration of about 3.7%formaldehyde and a pH of about 7.15. For histology purposes, thesolution also has desirable osmolality, osmolarity, and isotonicpressure which protects tissue to be fixed with the solution.

The kit 400 may be safely shipped, stored, and later combined with waterto form a solution of about 3.7% formaldehyde which contains no chemicalcontaminants, such as methanol.

It will be understood that the above examples are for explanationpurposes only, and other solid forms of polymerized aldehydes, buffers,and/or stabilizers may be used at different amounts and/or ratios.Additionally, kit 400 may contain other amounts and/or ratios than thosedescribed above which may mixed with different amounts of water toproduce larger or smaller amounts of a formaldehyde solution atdifferent concentrations.

Embodiments of the above described invention have several advantagesover current techniques of producing, transporting and storing aldehydesolutions. Transporting a powdered substance, which may be safely andeasily mixed with water by an end user after delivery, requires lessspace, is lighter (approximately twenty (20) times lighter than anaqueous solution of 37% paraformaldehyde), cheaper, and much safer totransport than the current practice of manufacturing a liquid aldehydesolution and then shipping the liquid solution to the end user.Additionally, a user can order a much larger quantity of the powderedsubstance and safely store it for an extended period of time, and in areduced amount of space, as compared to the amount of space required tostore the liquid solution.

It can be appreciated that other aldehydes can be prepared using thesame principles described herein. In general, any aldehyde that is solidunder the physical conditions of preparation and storage can be subjectto the methods of this invention. Examples of such suitable aldehydesinclude proprionaldehyde and acetaldehyde. Although glutaraldehyde andbutyraldehyde may be liquids under certain conditions, they may beprepared using the teachings of this invention.

Moreover, in addition to aldehydes, other fixatives may be prepared,stored and transported using the methods of this invention. Thus, osmiumtetraoxide, picric acid, potassium dichromate, mercuric chloride,potassium permanganate, and acrolein can be conveniently preparedaccording to this invention.

Any suitable buffer may be used to prepare the compositions of thisinvention. For many purposes, phosphate buffers or TRIS may be used.

In addition to buffers, one or more stabilizers may be used. Stabilizersinclude carboxypolysaccharides, by way of example,carboxymethylcellulose (CMC), hydroxymethylcellulose (HMC) and numerousother cellulose derivatives, as well as alginates, hyaluronates and thelike. Proteins can also be used as stabilizers, and include byway ofexample, gelatin. Additionally, pectin, carageenan, fatty acid ethers,hydrazine, hydroxylurea, urea, melamine and other acidicnitrogen-containing compounds, and hydrogen sulfide can also be used. Itcan be appreciated that other compounds having similar properties can beused in a composition of this invention as a stabilizer.

If desired, the above mixtures can be prepared in dried form and storedin a packet. Packets are convenient to store and weigh less thansolutions containing the same amounts of reactive agent, buffer and/orstabilizer. Thus, great savings of space, weight, transportation costs,as well as increased safety can be achieved using powdered forms. Inother embodiments, preparations can comprise two packets, in which afirst packet contains a fixative and a buffer, and a second packetcontains a powdered form of a stabilizer. Upon dissolving the firstpacket, a solution of a fixative in a buffer is obtained. In otherembodiments, a first packet can contain a fixative and a stabilizer ingranular form, and a second packet contains a buffer material, that upondissolving in aqueous solution, results in formation of a buffersolution having a desired pH and osmolarity.

It can be appreciated that after dissolution the contents of the packetsand mixing them together, the osmolarity can be further adjusted to adesired value, for example, 300 mOsm/L. It can also be appreciated thatagents that contribute to osmotic pressure can be included along withfixative, buffer, and/or stabilizer packets. Thus, it is convenient ifthe osmotic agent selected is also granular or powdered, and candissolve relatively rapidly in aqueous medium. Many such osmotic agentsare known in the art, but include sucrose and other sugars, salts, suchas NaCl and the like, numerous other small molecules, as well as largemolecules, such as proteins, complex carbohydrates and the like. Byadjusting the amounts of dry materials in a packet and by pre-selectingthe amount of aqueous medium added, the concentration, pH, osmolarityand/or other characteristic of a solution can be obtained.

It can also be appreciated that a first packet may contain a powdered orgranular fixative and a second packet may contain an additional bufferand/or stabilizer and/or osmotic agent. It is well known in the art toprepare various buffers as powders. By selecting the amounts of bufferpairs (e.g., sodium phosphate monobasic and sodium phosphate dibasic),the concentration and pH of the resulting solution can be achievedwithout the necessity of adjusting the pH after making the solution.Thus, use of the powdered formulations of this invention can be veryconvenient to use, in particular if large amounts of materials are used(e.g., as in industrial manufacturing applications).

Compositions of this invention are conveniently manufactured andtransported as kits. A kit can contain a first packet containingpowdered fixative (optionally, with buffer and/or stabilizer), a secondpacket (e.g., containing stabilizer and/or buffer and/or second buffer,and/or osmotic agent), and instructions for preparing liquid solutions.Optionally, a kit may contain measuring devices, cups, flasks, pipettes,and/or other equipment routinely used for making fixative solutions.

Uses of Powdered Compositions

In certain embodiments, powdered formalin or other histologicalfixatives find use in histology and other medically related fields.Thus, certain aldehehydes, picric acid, dichromates, permanganates andlike materials can be used for light microscopy, for example forhospital or clinical laboratory diagnostic procedures. Additionally,certain other fixatives, including permanganates, dichromates, osmiumtetroxide, uranyl acetate and the like may conveniently be used forelectron microscopic purposes, including medical diagnosis, laboratoryresearch and the like. In other embodiments, one or more of these heavymetal materials can be prepared as a second packet.

In addition, in other embodiments, compositions and methods of thisinvention can be suitably used for any industrial purpose in which areactant, such as an aldehyde is used. For example, numerous uses offormaldehyde are know in the art and are included in Formaldehyde, ThirdEdition, J. Frederic Walker, Reinhold Publishing Corporation, New York,1964, incorporated herein fully by reference, in particular, Chapter 20,pp. 552-660. A brief list of industries and/or uses of formaldehydepreparations of this invention includes manufacture of acetal resins,agriculture, analysis, catalysts, concrete, plaster and relatedproducts, cosmetics, deodorization, disinfection and fumigation, dyesand dye-house chemicals, embalming and preserving, explosives,fireproofing, fuels, gas absorbents, hydrocarbon products, insecticides,leather, fur and hair products, medicine, metal manufacturing, paper,photography, protein modification, rubber, solvents and plasticizers,stabilizers, starch, surface active agents (e.g., detergents), textilesand wood products.

Agricultural uses include formulation of slow release nitrogenfertilizers and for controlling microorganisms responsible for plantdiseases. Analytical uses include both quantitative and qualitativeanalysis of amino acid composition of proteins, analysis of nitrates,halogen acids, inorganic halides, alkali cyanides and numerous othernitrogen-containing materials, heavy metals, including gold, silvercopper and bismuth. Catalytic uses include preparation of hydrocarbons,alcohols and other products of hydrogenation. Additional uses includemanufacture of cement and other concrete products and plaster. Formalinis also a deodorant, and has uses in mouthwashes, soaps and germicides,used alone or with phenols. Formaldehyde can react with ammonia, amines,hydrogen sulfide, mercaptans, and other materials that have strongand/or offensive odors. Aldehydes can cross-link proteins together, andthus, can destroy bacteria, fungi, molds and yeasts. Formaldehyde iswidely used as an embalming agent and for preserving tissues for laterstudy. As indicated above, powdered formaldehyde preparations of thisinvention find wide use in hospitals and laboratories. Formaldehyde alsofinds significant use in the manufacture of explosives, where thealdehyde can be reacted with nitrogen-containing or oxygen-containingcompounds to form materials that can liberate a large amount of energyupon detonation. In some cases, formaldehyde can be used to stabilizewhat would otherwise be unstable explosives. In the petroleumindustries, formaldehyde finds use in drilling and operation of oilwells, in purification, modification and refining of petroleum fractionsand the synthesis of antioxidants. In the leather and hide industries,formaldehyde is widely used in tanning and in preparation of hairproducts for felting and dyeing. In the metal industries, formaldehydecan be used as acid inhibitors, reducing agents and electroplatingagents.

It should be understood that the particular embodiments described aboveare only illustrative of the principles of the present invention, andvarious modifications could be made by those skilled in the art withoutdeparting from the scope and spirit of the invention. Thus, the scope ofthe present invention is limited only by the claims that follow:

INDUSTRIAL APPLICABILITY

Embodiments of powdered formulations of aldehydes find use at least inindustries involving agriculture, analysis, catalysts, concrete, plasterand related products, cosmetics, deodorization, disinfection andfumigation, dyes and dye-house chemicals, embalming and preserving,explosives, fireproofing, fuels, gas absorbents, hydrocarbon products,insecticides, leather, fur and hair products, medicine, metalmanufacturing, paper, photography, protein modification, rubber,solvents and plasticizers, stabilizers, starch, surface active agents,textiles or wood products.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the invention.

1. A composition of matter comprising: an aqueous solvent; adepolymerized aldehyde; and, a stabilizer.
 2. The composition of matterof claim 1, wherein the aqueous solvent is water.
 3. The composition ofmatter of claim 1, wherein the depolymerized aldehyde is formaldehyde.4. The composition of matter of claim 1, wherein the stabilizer ishydroxypropyl methyl cellulose.
 5. A method for using powderedformaldehyde as a histological fixative, comprising the steps of: (a)providing a first material comprising powdered formaldehyde and a basiccomponent of a buffer pair; (b) providing a second material comprisingan acidic component of a buffer pair; (c) making a first aqueoussolution of said first material; (d) making a second aqueous solution ofsaid second material; (e) mixing said first and said second solutions;and (f) applying said solution obtained in step (c) to a piece of tissueuntil said tissue has become fixed.
 6. A method for producing anon-liquid composition of an aldehyde, comprising the steps of: (a)selecting a non-liquid aldehyde; (b) selecting a non-liquid buffer pairhaving an acidic member and a basic member of said pair; and (c) mixingsaid aldehyde and said basic member of said buffer pair together to forma mixture.
 7. The method of claim 6, further comprising adding anon-liquid stabilizer.
 8. The method of claim 6, further comprisingpulverizing said mixture.